This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Hydrocarbon producing gas wells generally produce liquids in addition to the flowing gas stream. These fluids, gas and liquids, are conducted to the surface by a string of production tubing that communicates the below ground formation to a piping system at the surface. Removal of the liquid fraction of the fluid column is mandatory for maintaining the unrestricted production of gas from the production zone formation. Frequently, a beam pump unit is employed for this task. However, beam pumping units are expensive and suffer from high maintenance costs.
In the field of plunger lift, a plunger acts as an unattached piston within the length of the production tubing for the purpose of lifting liquids from an active, gaseous hydrocarbon-bearing formation. In the life cycle of a plunger lift system, the plunger travels first downwardly to the bottom region of the tubing string adjacent to the formation then upwardly within the tubing string multiple times within the course of the day. The use of a plunger within the tubing conduit of a gas well will enable the upward flow of light-density gas to push toward the surface those heavier liquids within the tubing string.
Plunger movement is controlled by one or more flow control valves located between the upper end of this tubing conduit and the surface piping arrangement. Whenever a flow control valve at the surface is closed, the flow of fluids from the near-surface wellbore is terminated. At this point and by the force of gravity, the plunger within the tubing falls to the bottom of the production string within the wellbore where it typically encounters a shock-spring arrangement approximate the end of the tubing string. As the plunger falls, it encounters gas and liquid within the tubing. Being lighter relative to the plunger, these fluids are displaced around the plunger to a position above the falling plunger device. This migration is made possible by the undersized dimension of the piston-like plunger. In bypass plungers, the gas and liquid migrate up through an open central passageway within the plunger during descent
Later, once flow is reestablished at the surface, a plunger will begin its return to its uppermost range at the upper end of the tubing string. A plunger is forced to the surface by the up-flowing gas stream below it. As the plunger migrates upwardly, it pushes to the surface any liquid above the plunger and ahead of the gas column that is expanding from below the plunger.
There exist three plunger styles, the solid, one-piece plunger (non-bypass), the bypass plunger with an internal valve element and the two-piece bypass plunger. The effectiveness of each of these plungers is a function of its sealing element. The sealing elements of the several plunger iterations within the art vary in design and efficiency. There exist two common and one less common external sealing mechanism: the spiral groove design; the pad sealing element; and the less common elastomeric sealing elements. Any of these three sealing means listed can be used in conjunction with any of the three plunger styles.
A two-piece plunger will not return toward the surface until it first comes into contact with and joins to its external valve element, generally a spherical ball. Classified as one-piece plungers, both the dart plunger and the captured rod plunger have an internal valve element that is shifted into the closed position as these bypass plungers reach the bottom spring stop arrangement adjacent the end of the tubing. Once this internal valve is shifted to a closed position, these bypass style plungers will return to the surface, carried by the up-flowing gas stream.
The common spiral plunger is a solid one-piece design without an internal passageway. The common spiral plunger typically has concentric grooves arrayed along its length. It fits within the tubing string somewhat loosely per the requirements specified within the industry. The industry standards ensure that the purposefully undersized plunger will not become lodged within the tubing string. The pad style plunger and its sealing element fit more snugly within the tubing string and constitute a superior seal as compared to the spiral plunger. Because the sealing elements of the pad plunger are biased outwardly by springs, the larger pad plunger will not become wedged within the tubing.